Phase petrology, geochemistry and evolution of the ultrabasic-carbonatitic Blue Hills complex (Southern Namibia)

The ultrabasic, hypabyssal Blue Hills complex in Southern Namibia comprises a suite of highly silica undersaturated magmatic rocks, which are investigated by microprobe and geochemical bulk-rock analyses. The parental magma of these rocks formed by buffered melting at temperatures of 1100-1270 degrees C in a magma chamber at a depth of 100-110 km. During its ascent, magmatic differentiation and loss of volatiles led to the genesis of more differentiated rock types of the ultrabasic suite culminating in the formation of carbonatites and a pegmatite. On the basis of their geochemistry, we describe the relationships between these rocks and present a model for the formation of the complex. In addition, a short description of the petrography and the phase relations is presented together with a comparison with kimberlites and other ultrabasic rocks.